This cat litter calculator works out how much litter your boxes go through in a month from their size, how deep you fill them and how often you empty them, then turns that into bags and money at the price you pay. Your numbers stay on your screen: nothing you type leaves the page.
Apartment Cats earns a commission when you buy through the Amazon links on this page, at no cost to you. Picks are made on published specs, never on commission. How this works
This tool runs on JavaScript. To work it out by hand, multiply a box’s inside length, width and litter depth in inches, divide by 61 for liters, multiply by the number of boxes, then by the full changes you make in a month.
What to buy for this answer
These come from the picks in our published litter guides and change with your answer: at your monthly amount, the first card is the closest match.
Tidy Cats LightWeight Free & Clean Unscented
- What it is
- Unscented clumping clay made light, in an 8.5 lb jug, a 12 lb box and 17 lb pails or boxes.
- Why it fits
- That load is the reason to switch: Purina says its 8.5 lb jug covers as much box as 20 lb of ordinary clumping clay.
- Skip if
- Your cat uses its box happily now; any change of litter goes slowly, one thing at a time.
Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.Whisker Litter-Robot 4
- What it is
- A self-cleaning globe box by Whisker that stands 29.5 in (75 cm) tall on a 22 by 27 in floor (56 by 69 cm).
- Why it fits
- For two or more cats: Whisker rates it for as many as four cats, each between 3 and 25 lb, on clumping litter, with standard-weight clay recommended.
- Skip if
- The only free spot is a damp bathroom, which Whisker warns against. It still counts as one box, and no veterinary guideline takes a side on self-cleaning boxes.
Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.IRIS USA XL Open-Top with Shield
- What it is
- An open-top box by IRIS with a raised back and sides: 30.2 in long and 20 in wide outside (77 by 51 cm), 13.1 in (33 cm) high.
- Why it fits
- A short box, or one box too few: on the 1.5 times rule its outside length suits a cat up to about 20 in (51 cm).
- Skip if
- Your cat is older or stiff in the hips: IRIS gives no height for the way in.
Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.Cat’s Pride Max Power Total Odor Control Unscented
- What it is
- Unscented clumping clay, a blend of two clays, in a 15 lb jug by the listing.
- Why it fits
- You want to stay on regular clay: its maker lists it 25% lighter than traditional scoopable clay and 99% dust free.
- Skip if
- Every pound counts on your stairs, where the lightweight clays claim about half.
Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.World’s Best Multiple Cat Unscented
- What it is
- Clumping whole-kernel corn, unscented, here in 15 lb (sizes run from 8 to 32 lb), by its maker.
- Why it fits
- For a home with more than one cat or a plant litter: the maker counts a 15 lb bag as 36 days or more for two cats.
- Skip if
- You would mix it with a non-clumping litter, which the listing says not to do.
Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.SmartCat All Natural Clumping
- What it is
- Clumping grass litter grown on US farms and sold fragrance-free, in 5, 10 and 20 lb bags.
- Why it fits
- A plant litter that its maker says weighs half as much as clay clumping litter, listed 99% dust free.
- Skip if
- Tracking already bothers you: the maker itself suggests a rug by the box.
Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.Small Pet Select Pelleted Pine
- What it is
- Non-clumping pellets of virgin pine with nothing added, in 8, 20 and 40 lb, by its maker.
- Why it fits
- You picked pine: the pellets turn to sawdust, so a sifting box keeps the whole ones and tells you when to empty.
- Skip if
- You run a self-cleaning globe: Whisker says pellets will not sift in a Litter-Robot.
Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.PetSafe ScoopFree Premium Crystal Litter
- What it is
- Non-clumping silica crystals in two pre-portioned 4.3 lb bags, by PetSafe.
- Why it fits
- PetSafe’s own figure is a month at most per bag with one cat, a claim to hold up against your answer.
- Skip if
- You want no scent: it is sold lightly scented, and veterinary guidelines advise unscented litter.
Details
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.How the cat litter calculator works
Four steps, all plain arithmetic, in this order:
- One fill: inside length times width times litter depth. A 24 by 16 in (61 by 41 cm) box filled 2 in (5.1 cm) deep holds 768 cubic inches, which is 12.6 liters.
- A month: that fill times your boxes, times the full changes in 30.4 days.
- Weight: liters times pounds per liter, where a source or your own bag gives one.
- Bags and money: the monthly amount over your bag size gives the bags a month and how long one bag of litter lasts; times your price, it gives the litter cost per month, and times 12, the year.
Type over any starting value, or arrive from the litter depth check in the cat measuring tool, which brings your box size and depth along.
How much cat litter per month, and why it is a range
Scooping takes out waste. Full changes are what empty the bag. The guidelines disagree on how often to do them for clumping litter: the AAFP and ISFM give every 1 to 4 weeks, iCatCare every 1 to 2, and Nebraska Humane Society about every 2. Where they overlap, 1 to 2 weeks, the answer doubles from one end to the other, so the calculator shows both ends instead of picking a number for you. San Diego Humane Society empties non-clumping litter every 2 to 3 days, which is one of the routines you can choose.
The box count matters as much. One box per cat plus one is the AAHA and AAFP rule of thumb, so a single cat starts with two, and each one is filled and emptied. That is why the first answer, about 55 to 109 liters a month, is more than many owners expect. Top-ups after scooping come on top; no source we found puts a number on them, so the field takes yours.
Where the pounds come from
The clay litter pages we read give each bag’s weight and never its volume, so pounds need a figure for how heavy a liter is. For regular clumping clay the calculator uses Whisker’s: the maker of the Litter-Robot lists a gallon (4 L) of clumping litter at about 8 to 10 lb, and warns that weight varies by brand. That makes the example box about 25 to 31 lb per fill.
Lightweight clay is where the claims run loose. Tidy Cats says 8.5 lb of its lightweight litter equals 20 lb of regular, Fresh Step pairs an 11.5 lb jug with a 22 lb carton, Arm & Hammer says 50% lighter and Cat’s Pride says 25% lighter. Each measures against a different yardstick, so the calculator shows that spread only as a comparison under clumping clay. For pine pellets, other plant litters and crystals we found no weight per liter at all. Enter the volume printed on your bag, or fill a 1-quart jug with your litter and weigh it on a kitchen scale.
If you live in a walk-up, read the carried-home line before the cost. A full month of clumping clay for two boxes can pass 200 lb, and the lightweight litter guide compares the bags that cut that load. We publish no litter prices: they change by store and by week, and the one on your receipt is the only figure that fits your budget.
Cat litter questions, answered with numbers
How much cat litter do I need per month?
It depends on box size, depth and how often you empty everything. One cat with two 24 by 16 in (61 by 41 cm) boxes kept 2 in (5.1 cm) deep, changed every 1 to 2 weeks, goes through roughly 55 to 109 liters, or 109 to 273 lb of clumping clay. A smaller box or a 1.5 in (3.8 cm) fill shrinks it.
How long should a 20 pound bag of litter last?
By Whisker’s figure, 20 lb of clumping clay is about 8 to 10 liters, close to one fill of an 18 by 14 in (46 by 36 cm) box at 2 in (5.1 cm) deep (8.3 liters). Emptying that single box every 1 to 2 weeks, the bag covers about 1 to 2.5 weeks. A second box halves that.
How much litter should be in the box?
Cornell’s Feline Health Center puts it at about 1 to 2 inches (2.5 to 5.1 cm) for most cats, while the AAFP and ISFM guidelines put the minimum near 1.25 in (3 cm). Deeper does not mean less scooping, Nebraska Humane Society notes. It does cost more: on any box, going from 1.5 to 2 in (3.8 to 5.1 cm) adds a third to every fill.
How much does cat litter cost?
That turns on two things only you know: your price per bag and what your routine uses. Prices swing between stores and weeks, so we print no average. Type your bag size and price above, and the calculator turns the bags a month into your litter cost per month at that price, then multiplies by 12 for a year.
How many gallons is 40 lb of cat litter?
For regular clumping clay, about 4 to 5 gallons, using Whisker’s 8 to 10 lb per gallon. Lightweight clay fills more gallons for the same 40 lb, by its makers’ claims, and pine or crystal litter could differ either way. If your bag prints its volume, put that in the calculator instead of the weight.
Does the extra box double what I carry home?
For full changes, yes in practice: every box gets filled and emptied on its own schedule, so two boxes of the same size take twice the litter of one. Keep the second box anyway, since the count rule exists for the cat. A smaller second box, or a fill nearer 1.5 in (3.8 cm), trims the load on the stairs.
Sources
- Cornell Feline Health Center, Feline behavior problems: house soiling. Read Oct 16, 2026.
- AAFP and ISFM, Guidelines for diagnosing and solving house-soiling behavior in cats, Journal of Feline Medicine and Surgery, 2014. Read Oct 16, 2026.
- AAHA and AAFP, 2021 Feline Life Stage Guidelines: general litter box considerations. Read Oct 16, 2026.
- iCatCare, Consensus guidelines on lower urinary tract diseases in cats, JFMS 2025. Read Oct 16, 2026.
- Nebraska Humane Society, Litter box set-up. Read Oct 16, 2026.
- San Diego Humane Society, Litter boxes 101. Read Oct 16, 2026.
- Whisker, How much litter do I put in Litter-Robot? Read Oct 17, 2026.
- Lightweight weight claims on the makers’ pages: Tidy Cats, Fresh Step, Arm & Hammer and Cat’s Pride. Read Oct 16, 2026.
Related: all the litter guides, the types of litter compared, the cat measuring tool and the printable litter and cleaning tracker for logging a real month.